The present invention relates to video signal processing apparatuses and, more particularly, to a video signal processing apparatus that reduces the quantity of data which have been digitized and compressively coded.
When a video which is an analog signal is digitized to be handled as a digital video signal, it can be handled integrally with digitized audio signal, character data, program and the like and, moreover, data processing such as data compression or encryption is easily carried out.
Image data of a digital video signal or the like is an array of pixels which are discrete digital data having pixel values indicating luminance and chrominance, and it is processed for every frame corresponding to one image. When image data of each frame is compressively coded for recording or transmission, intra-frame coding based on spatial correlation within one frame is performed, and the compression ratio can be increased by performing, as well as intra-frame coding, inter-frame coding based on temporal correlation between frames which are close each other in time series. According to intra-frame coding, I pictures, which can be decoded independently, are obtained. According to inter-frame coding, P pictures are obtained by performing prediction in the forward direction while B pictures are obtained by performing prediction in both of the forward and backward directions. Although the compression ratio of the P or B pictures is increased by processing the difference data, these pictures cannot be decoded independently.
In a general compressive coding technique such as MPEG, discrete cosine transform (DCT) is carried out. DCT is performed on each pixel block comprising a predetermined number of pixels. In the state before DCT, the pixel values are randomly distributed over the pixel block. However, in DCT coefficients obtained as the result of DCT, large pixel values are unevenly distributed in a low frequency band. So, the DCT coefficients are subjected to quantization (i.e., division) to make the values of high-band components 0, and further subjected to variable-length coding based on a series of the same value, thereby obtaining compressed variable-length code ward data. Usually, the variable-length code word data is recorded or transmitted.
When recording such digitized and compressively coded data in a recording medium, a transparent recording method represented by MPEG2-TS is used as well as a base band recording method which has conventionally been used. According to the transparent recording method, data (e.g., variable-length code word data) transmitted as a bit stream is recorded as it is and, therefore, this method has the advantage of needing no encoder or decoder for a digital video signal, and keeping the image quality of the transmitted data as it is.
As an example of a recording medium used for recording and retaining a digital video signal, there is a digital video cassette tape. In xe2x80x9cDVB (Digital Video Broadcasting) Signal Recording DVCR (Digital Video Cassette Recorder) Standardxe2x80x9d by HD-DVCR conference held at December 1995, a recording format for a digital TV broadcast signal processed in accordance with MPEG is standardized, and this standard includes, as an option, the standard of recording of data for trick play (TP). Hereinafter, a description is given of recording of data for rapid play in this standard.
It is assumed that two kinds of data for rapid play having different search speeds are to be recorded. When recording data on a tape record medium, a signal is recorded on part called tracks. The data for rapid play is repeatedly recorded on plural tracks so that it can be searched at a high speed. Therefore, the maximum search speed is decided according to the number of repetitions of recording. Here, it is assumed that TPH data which can be read at a search speed 18 times as high as the normal speed at the maximum, and TPL data which can be read at a search speed 4 times as high as the normal speed at the maximum, are recorded.
FIG. 14 is a diagram for explaining recording of such data on a tape record medium, illustrating a track pattern of a DVCR in which MPEG2-TS data is allocated on a tape. As shown in FIG. 14, in this track format, a unit comprising four tracks (F0, F1, F0, F2) is repeated. When data for trick play (rapid play) is recorded in this format (since it is an option as mentioned above), the data should be allocated in a specific position in the tape.
Data to be recorded in the tape is based on a sync block of a fixed data quantity, and the data for rapid play is recorded for every five sync blocks in a specific position in a video data recording area shown in FIG. 14. To be specific, TPH data is recorded in positions on the F0 track, which positions are indicated by sync block numbers 40-44, 62-66, 84-88, 106-110, 128-132, and 150-154, that is, it is recorded in 30 sync blocks in total (5 sync blocksxc3x976 positions). Further, TPL data is recorded in a position in the F1 track, which position is indicated by sync block numbers 131-155, that is, it is recorded in 25 sync blocks.
As described above, in this standard, recording of data for trick play is an option, so that sync block extra headers given to the respective sync blocks are used for identification of data recorded in the above-mentioned positions. FIG. 15 shows the state of a sync block extra header given to data for rapid play. The sync block extra header is a 1-byte header included in each sync block, and one bit shown by b7 in the figure is used to distinguish between data for normal-speed play and data for rapid play. In FIG. 15, the value of b7 is 1, and this indicates that the sync block is data for trick play (rapid play).
Amongst the other bits composing the sync block extra header, one bit shown by b6 is a bit used for deciding whether the sync block is new frame data or not, and this is a bit of a frame toggle used as a toggle. It is defined that frame toggling should not be performed more than two times within one track. Bits shown by b2-b5 are used as a counter for distinguishing areas of data for trick play. Further, b0 and b1 are reserved.
As described above, in the DVCR, data for rapid play is recorded in a specific position in accordance with the optional standard, and the effect that the data recorded in that position is data for trick play (rapid play) is identified by the header.
As described above, when handling digital video data, the data is compressively coded by DCT, quantization, and variable-length coding, to be recorded or transmitted. Since variable-length code ward data obtained through these processes includes high-band (high-frequency) components of DCT coefficients, it is possible to reduce the data quantity for recording or transmission by removing the high-band components which have less influence on the quality of reproduced image. However, such reduction of data quantity has hardly been performed.
A thinkable method for reducing the data quantity is as follows. That is, variable-length code word data (digital data) is once analogized, and high-band components are removed from the analog signal and, thereafter, the analog signal is again digitized to obtain variable-length code word data. According to this method, high-band components are appropriately removed from the variable-length code word data to reduce the data quantity. In this method, however, since the reverse processes of digitization and compressive coding to generate the variable-length code word data are performed and then further digitization and compressive coding are performed, the circuit scale and the processing time are increased. Especially the circuit scale and the number of processes for the digital-to-analog conversion are considerable, it is not practical to reduce the data quantity according to this method.
Further, in the case where the digital data so obtained is recorded on a tape record medium or the like by the above-mentioned transparent recording method, when the digital data is recorded as data for trick play such as rapid play, the image quality is significantly degraded at the time of trick play. The reason is as follows. According to the transparent recording method, the above-mentioned I, P, or B picture is recorded as it is. So, if the P or B picture which is not assumed to be decoded independently is used as data for rapid play, loss of data is considerable.
Accordingly, if only I pictures are extracted to be used, available data for rapid play is obtained. However, in the recording format of the tape record medium, since the positions to record the data for trick play are specified as shown in FIG. 14, in order to secure a practical update cycle, it is desirable to reduce the data quantity of the I pictures, without recording every I picture. In this case, to simplify the procedure, one I picture is selected from several I pictures, and this is used as data for rapid play.
However, when the data for rapid play generated as described above is reproduced for display, since the display lacks the information of motion, satisfactory display result is not obtained. Therefore, it is preferable to reduce the data quantity in every I picture so as to obtain data for rapid play which can transmit the information of motion, although such reduction is attended with some degradation in image quality. However, such a method for reducing the data quantity has not been proposed in the video signal processing according to the prior arts.
It is an object of the present invention to provide a video signal processing apparatus which can reduce the quantity of variable-length code word data without significantly degrading the quality of reproduced image.
It is another object of the present invention to provide a video signal processing apparatus which enables recording of data for rapid play on a tape record medium or the like, with reduced data quantity, without significantly degrading the quality of reproduced image.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the scope of the invention will be apparent to those of skill in the art from the detailed description.
According to a first aspect of the present invention, a video signal processing apparatus for processing coded data obtained by compressively coding a digitized video signal, includes specific component removing means for removing specific components in the coded data. Therefore, the data quantity of the coded data can be reduced by removing specific components of the coded data, which components have less influence on the quality of the reproduced image.
According to a second aspect of the present invention, in the video signal processing apparatus of the first aspect, the coded data to be processed is obtained by variable-length coding, and the specific component removing means removes, as the specific components, high-band components included in the variable-length coded data. Therefore, the data quantity of the variable-length coded data can be reduced by removing specific components of the variable-length coded data, which components have less influence on the quality of the reproduced image.
According to a third aspect of the present invention, in the video signal processing apparatus of the second aspect, the specific component removing means comprises variable-length decoding means for subjecting the variable-length coded data to variable-length decoding; inverse quantization means for inversely quantizing the processing result of the variable-length decoding means, by using a first quantization matrix; quantization means for quantizing the processing result of the inverse quantization means, by using a second quantization matrix; and variable-length coding means for subjecting the processing result of the quantization means to variable-length coding. Therefore, the data quantity of the variable-length coded data can be reduced by removing specific components of the variable-length coded data, which components have less influence on the quality of the reproduced image, without performing digital to analog conversion which causes an increase in circuit scale, whereby flexible setting is realized in the data removal process.
According to a fourth aspect of the present invention, in the video signal processing apparatus of the second aspect, the specific component removing means comprises variable-length decoding means for subjecting the variable-length coded data to variable-length decoding; decoding result processing means for subjecting the processing result of the variable-length decoding means to a process of changing the value of a specific part constituting the processing result; and variable-length coding means for subjecting the processing result of the decoding result processing means to variable-length coding. Therefore, the data quantity of the variable-length coded data can be reduced by removing specific components of the variable-length coded data, which components have less influence on the quality of the reproduced image, without performing digital to analog conversion which causes an increase in circuit scale, whereby the circuit scale is further reduced as compared with the apparatus of the fourth aspect.
According to a fifth aspect of the present invention, in the video signal processing apparatus of the second aspect, the specific component removing means comprises coding characteristic detecting means for detecting the characteristics of variable-length codes composing the variable-length coded data, from the variable-length coded data; and specific code removing means for removing specific codes included in the variable-length coded data, in accordance with the characteristics of the variable-length codes detected by the coding characteristic detecting means. Therefore, the data quantity of the variable-length coded data can be reduced by removing specific components of the variable-length coded data, which components have less influence on the quality of the reproduced image, without performing digital to analog conversion which causes an increase in circuit scale, whereby the circuit scale is further reduced as compared with the apparatus of the fourth aspect.
According to a sixth aspect of the present invention, in the image signal processing apparatus of the fifth aspect, the specific component removing means removes the specific variable-length codes by performing the following processes: code length reading process for reading the code lengths of the variable-length codes composing the variable-length coded data; sum total calculating process for accumulatively summing the code lengths read in the code length reading process to obtain the sum total of the code lengths; and variable-length code outputting process for comparing the sum total of the code lengths obtained in the sum total calculating process with a predetermined threshold, and outputting variable-length codes of a code length lower than the threshold, in accordance with the result of the comparison. Since the data quantity of the variable-length coded data is reduced so that its code length does not exceed a predetermined code length, the apparatus performs appropriately when it is desired that the data quantity should be within a set value.
According to a seventh aspect of the present invention, in the video signal processing apparatus of the fifth aspect, the specific component removing means removes the specific variable-length codes by performing the following processes: number obtaining process for obtaining the number of unit data included in variable-length codes composing the variable-length coded data; sum total calculating process for accumulatively summing the numbers of unit data obtained in the number obtaining process, to obtain the sum total of unit data; and variable-length code outputting process for comparing the sum total of the numbers of unit data obtained in the number obtaining process with a predetermined threshold, and outputting variable-length codes having the number of unit data lower than the threshold, in accordance with the result of the comparison. Since the data quantity of the variable-length coded data is reduced so that it has unit data (DCT coefficients) within a predetermined number, this apparatus performs appropriately when a reproduced image with less distortion is desired.
According to an eighth aspect of the present invention, in the video signal processing apparatus of the second aspect, the specific component removing means comprises: digital video signal generating means for generating a digital video signal from the variable-length coded data; specific digital signal removing means for removing a specific part of the digital video signal, from the digital video signal generated by the digital video signal generating means; variable-length coded data generating means for generating variable-length coded data from the processing result of the specific digital signal removing means; and quantization matrix holding means for holding a quantization matrix used for both of the process in the digital video signal generating means and the process in the variable-length coded data generating means. Therefore, the data quantity of the variable-length coded data can be reduced by removing specific components of the variable-length coded data, which components have less influence on the quality of the reproduced image, without performing digital to analog conversion which causes an increase in circuit scale, whereby more flexible setting is achieved as compared with the apparatus of the first aspect.
According to a ninth aspect of the present invention, in the video signal processing apparatus of the first aspect, the coded data to be processed is obtained by intra-frame coding and inter-frame coding, and the specific component removing means removes, as the specific components, high-band components included in the intra-frame coded data amongst the coded data to be processed. Therefore, the data quantity of the intra-frame coded data can be reduced by removing components of the data, which components have less influence on the quality of the reproduced image.
According to a tenth aspect of the present invention, the video signal processing apparatus of the ninth aspect further includes intra-frame coded part extracting means for extracting intra-frame coded data from the coded data to be processed; data holding means for temporarily holding the data; reading indication signal generating means for generating a signal which indicates a timing to read the data held in the data holding means; and data reading control means for controlling reading of data held in the data holding means, in accordance with the signal generated by the reading indication signal generating means. Therefore, the data quantity is reduced and, moreover, it is possible to generate data which can be appropriately recorded in a record medium outside the apparatus in accordance with the readout timing.
According to an eleventh aspect of the present invention, in the video signal processing apparatus of the tenth aspect, the specific component removing means removes the specific components from the processing result of the intra-frame coded part extracting means, and the data holding means holds the processing result of the specific component removing means. Therefore, the above-described effects are obtained.
According to a twelfth aspect of the present invention, in the video signal processing apparatus of the eleventh aspect, the specific component removing means comprises first specific component removing means for removing the specific components from the processing result of the intra-frame coded part extracting means, in accordance with a first characteristic value, and second specific component removing means for removing the specific components from the processing result of the intra-frame coded part extracting means, in accordance with a second characteristic value; the data holding means comprises first data holding means for holding the processing result of the first specific component removing means, and second data holding means for holding the processing result of the second specific component removing means; and the data reading control means comprises first data reading control means for controlling reading of data from the first data holding means, and second data reading control means for controlling reading of data from the second data holding means. Therefore, it is possible to generate two kinds of data having different degrees of data reduction.
According to a thirteenth aspect of the present invention, in the video signal processing apparatus of the tenth aspect, the data holding means holds the processing result of the intra-frame coded part extracting means, and the specific component removing means removes the specific components from the data held by the data holding means. Therefore, the above-described effects are obtained.
According to a fourteenth aspect of the present invention, the video signal processing apparatus of the thirteenth aspect further includes removal characteristic decision means for deciding a characteristic value used for removal of the specific components by the specific component removing means; and the specific component removing means removing the specific components in accordance with the characteristic value decided by the removal characteristic decision means. Therefore, it is possible to generate data having different degrees of data reduction.